Carrier particles for sorptive impregnants are known. Exemplary are conventional sorptive impregnants such as copper and silver salts, on activated carbon particles.
Fibrous structures containing functionally active particles are commercially available. Filter media or filters made from these structures include sorptive particles for selectively removing certain components of a liquid or gas passing through the filter. Acceptable performance with low pressure drop beneficially results from the active particles being distributed in a three dimensionally spaced apart arrangement. Advantageously, the supporting fibrous structure is stabilized by fiber-fiber bonding, and the active particles are bonded to, or entrapped in interstitial spaces of, the fibrous structure.
Fine active particles will beneficially provide more surface area for a desired end use than a comparable volume of larger particles, but there must be accessibility to the fine particles by a gas or liquid being passed through the fibrous structure. Difficulties exist when active particles are fine, in particular submicron in size. For example, control of the movement of fine particles when introducing fine particles into or onto a fibrous structure, is challenging because of the mobility or irregular motion of fine particles. Fine, mobile particles also tend to cover available fibrous surface area, and thus may interfere with subsequent fiber-fiber bonding.
Immobilization of fine, mobile particles to prevent loss during use is highly desirable. The immobilization requires adequate surface area for deposition of the fine particles. However, an equivalent volume of fine particles requires more surface area for deposition than would be required by an equivalent volume of conventionally-sized particles, for instance, having an average diameter in the range of approximately 300 to 500 microns. Enough fiber surface will typically not be available in a fibrous structure of macrofibers, for surface bonding of a useful loading of fine active particles. Additionally, the need for the fibrous structure to have an acceptably low pressure drop will typically conflict with enough fiber surface. Moreover, even if excess fiber surface were available, the immobilization must be efficient so that loss during use will be minimized.
Accordingly, an improved fibrous structure having a three dimensional arrangement of immobilized active material, is needed. Such a fibrous structure would benefit the use, and provide increased surface for the immobilization, of fine, mobile particles as the active material, but nevertheless have acceptably low pressure drop. Such a fibrous structure would advantageously provide accessibility of fine active particles to a gas or liquid being passed through the fibrous structure, yet minimize the loss of fine active particles during use.